The present invention relates to low loss buffered glass optical waveguide fibers.
Recent advances in the fabrication of optical fibers from ultratransparent materials have caused such fibers to be a promising transmission medium for optical communication systems. To be acceptable for use in optical communication systems, these light transmitting fibers, which are referred to as optical waveguides, should exhibit low signal attenuation, preferably below 10dB/kilometer. In the transmission of such light signals, which may consist of visible or invisible light, such signals are readily attenuated in response to relatively small distortions of the optical waveguide. For example, relatively sharp bends, or a rough adjacent surface may produce sufficient distortions within the optical waveguide to result in totally unacceptable signal attenuation. Similarily, transverse or longitudinal stresses imposed upon the optical waveguide fibers during cable construction or inherent in the resulting structure may produce totally unacceptable signal attenuation in the resulting cable. The loss of signal due to microbending of optical fibers caused by the irregularities at the interface between the fiber and its surrounding has been somewhat alleviated by the application of a plastic jacket to the fiber immediately after the fiber is drawn. U.S. patent application Ser. No. 692,895 filed in the name of S. A. Claypoole et al. on June 4, 1976 and assigned to a common assignee, which application is a continuation-in-part of application Ser. No. 593,286 filed July 7, 1975, now abandoned, teaches the application of a release agent to the optical waveguide fiber followed by the application of a thermoplastic coating for the purpose of increasing fiber strength and decreasing signal attenuation due to forming a plurality of such buffered fibers into an optical waveguide fiber cable.
The publication by D. Gloge entitled "Optical-Fiber Packaging and Its Influence on Fiber Straightness and Loss" Bell System Technical Journal, Vol. 54, No. 2, Feb. 1975, pp. 245-262 discusses the reduction in fiber attenuation resulting from the application of various types of plastic coatings to the fiber. Gloge discusses the relative protection afforded by a soft plastic jacket, a hard plastic jacket, a hard plastic jacket padded with a thin layer of soft plastic material or a shell of hard plastic material on top of soft plastic material. In his theoretical analysis of the protection afforded by multiple layer jackets, Gloge makes the assumption that if the outer jacket is the softer one and sufficiently thick that a deformation beyond its elastic limit is unlikely, the elastic modulus of the jacket is simply the modulus of the outer jacket material. This assumption is not justified and can result in an erroneous determination of the effects of such a double layer jacket.